Engine starting system and engine starting method

ABSTRACT

A starting system of an engine mounted in a vehicle capable of running using torque output from an electric motor includes a estimation portion that estimates engine speed and output torque of the engine when the engine is driven to realize the power requested by the driver, a comparing portion that compares a time for which the engine continues to be stopped with a first time and a second time that is longer than the first time, a first starting portion that starts the engine when estimated engine speed is greater than first speed and less than second speed, and the estimated output torque is greater than first value and less than second value, and a second starting portion that starts the engine when the time for which the engine continues to be stopped is longer than the second time.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2010-096747 filed onApr. 20, 2010, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an engine starting system and an enginestarting method. More particularly, the invention relates to technologyfor starting an engine mounted in a vehicle that is able to run usingtorque output from an electric motor.

2. Description of the Related Art

A hybrid vehicle provided with an engine and an electric motor as drivesources is known. The hybrid vehicle is provided with a power storagedevice such as a battery that stores electric power to be supplied tothe electric motor. Electric power generated by a generator driven bythe engine and electric power regenerated using the electric motorduring deceleration of the vehicle, for example, are stored in thebattery. In a plug-in hybrid vehicle, the battery is also able to becharged with electric power supplied from an external power supplyoutside the vehicle.

A hybrid vehicle is able to run using one or both of the engine and theelectric motor as the drive source according to the operating state ofthe vehicle and the like. Therefore, when the state-of-charge (SOC) ofthe battery is large, for example, the engine may be stopped and thevehicle may be run using only the electric motor as the drive source.The driver may also be able to select a mode to run using only theelectric motor as the drive source by operating a switch.

Therefore, in a hybrid vehicle, the time that the engine continues to bestopped, i.e., remains stopped, tends to be long. In particular, in aplug-in hybrid vehicle, if the battery is charged often using anexternal power supply outside the vehicle, there will be no need todrive the engine to generate power to charge the battery. Therefore, itis possible that the engine will almost never be driven. If the engineis not driven for an extended period of time, the amount of evaporatedfuel (vapor) from the fuel tank and the like that is trapped in acanister may become excessive. Also, lubrication may become insufficientbecause the oil pump is not driven. Therefore, technology that forciblydrives the engine at regular intervals has been proposed.

Japanese Patent Application Publication No. 5-270294 (JP-A-5-270294)describes a control apparatus for an electric vehicle, that forciblydrives an internal combustion engine when it is detected that theinternal combustion engine has not been used for a predetermined periodof time.

However, if the engine is driven at regular intervals, fuel efficiencymay decrease from driving the engine.

SUMMARY OF THE INVENTION

The invention thus provides an engine starting system and an enginestarting method capable of suppressing a decrease in fuel efficiency dueto forcibly driving an engine.

A first aspect of the invention relates to a starting system of anengine mounted in a vehicle capable of running using torque output froman electric motor. This starting system includes detection portion thatdetects power requested by a driver; estimation portion that estimatesengine speed and output torque of the engine when the engine is drivento realize the power requested by the driver; comparing portion thatcompares a time for which the engine continues to be stopped with afirst time and a second time that is longer than the first time;determining portion that determines whether the estimated engine speedis greater than a first speed and less than a second speed that isgreater than the first speed, and the estimated output torque is greaterthan a first value and less than a second value that is greater than thefirst value, when the time for which the engine continues to be stoppedis longer than the first time and shorter than the second time; firststarting portion that starts the engine when the estimated engine speedis greater than the first speed and less than the second speed, and theestimated output torque is greater than the first value and less thanthe second value; and second starting portion that starts the enginewhen the time for which the engine continues to be stopped is longerthan the second time.

According to this structure, if the time for which the engine continuesto be stopped is longer than the second time, the engine is forciblystarted. Meanwhile, if the engine speed is greater than the first speedand less than the second speed, and the output torque of the engine isgreater than the first value and less than the second value, when thetime for which the engine continues to be stopped is longer than thefirst time and shorter than the second time, the engine is started. As aresult, the engine can be driven in a fuel efficient operating range,for example. Therefore, a decrease in fuel efficiency due to forciblydriving the engine can be suppressed.

A second aspect of the invention relates to a starting system of anengine mounted in a vehicle capable of running using torque output froman electric motor. This starting system includes detection portion thatdetects power requested by a driver; estimation portion that estimatesefficiency of the engine when the engine is driven to realize the powerrequested by the driver; comparing portion that compares a time forwhich the engine continues to be stopped with a first time and a secondtime that is longer than the first time; determining portion thatdetermines whether the estimated efficiency is equal to or greater thana preset efficiency, when the time for which the engine continues to bestopped is longer than the first time and shorter than the second time;starting portion that starts the engine when the estimated efficiency isequal to or greater than the preset efficiency; and second startingportion that starts the engine when the time for which the enginecontinues to be stopped is longer than the second time.

According to this structure, if the time for which the engine continuesto be stopped is longer than the second time, the engine is forciblystarted. Meanwhile, if the efficiency of the engine is equal to orgreater than a preset efficiency when the time for which the enginecontinues to be stopped is longer than the first time and shorter thanthe second time, the engine is started. As a result, the engine can bedriven in a fuel efficient operating range. Therefore, a decrease infuel efficiency due to forcibly driving the engine can be suppressed.

A third aspect of the invention relates to a starting system of anengine mounted in a vehicle capable of running using torque output froman electric motor. This starting system includes detection portion thatdetects power requested by a driver; estimation portion that estimatesefficiency of a hybrid system that includes the electric motor and theengine, when the engine is driven to realize the power requested by thedriver; comparing portion that compares a time for which the enginecontinues to be stopped with a first time and a second time that islonger than the first time; determining portion that determines whetherthe estimated efficiency is equal to or greater than a presetefficiency, when the time for which the engine continues to be stoppedis longer than the first time and shorter than the second time; andsecond starting portion that starts the engine when the time for whichthe engine continues to be stopped is longer than the second time.

According to this structure, if the time for which the engine continuesto be stopped is longer than the second time, the engine is forciblystarted. Meanwhile, if the efficiency of the hybrid system that includesthe electric motor and the engine is equal to or greater than a presetefficiency when the time for which the engine continues to be stopped islonger than the first time and shorter than the second time, the engineis forcibly started. As a result, the engine can be forcibly driven inan operating range with good fuel efficiency for the vehicle as a whole.Therefore, a decrease in fuel efficiency due to forcibly driving theengine can be suppressed.

A fourth aspect of the invention relates to a starting method of anengine mounted in a vehicle capable of running using torque output froman electric motor. This starting method includes detecting powerrequested by a driver; estimating engine speed and output torque of theengine when the engine is driven to realize the power requested by thedriver; comparing a time for which the engine continues to be stoppedwith a first time and a second time that is longer than the first time;determining whether the estimated engine speed is greater than a firstspeed and less than a second speed that is greater than the first speed,and the estimated output torque is greater than a first value and lessthan a second value that is greater than the first value, when the timefor which the engine continues to be stopped is longer than the firsttime and shorter than the second time; starting the engine when theestimated engine speed is greater than the first speed and less than thesecond speed, and the estimated output torque is greater than the firstvalue and less than the second value; and starting the engine when thetime for which the engine continues to be stopped is longer than thesecond time.

A fifth aspect of the invention relates to a starting method of anengine mounted in a vehicle capable of running using torque output froman electric motor. This starting method includes detecting powerrequested by a driver; estimating efficiency of the engine when theengine is driven to realize the power requested by the driver; comparinga time for which the engine continues to be stopped with a first timeand a second time that is longer than the first time; determiningwhether the estimated efficiency is equal to or greater than a presetefficiency, when the time for which the engine continues to be stoppedis longer than the first time and shorter than the second time; startingthe engine when the estimated efficiency is equal to or greater than thepreset efficiency; and starting the engine when the time for which theengine continues to be stopped is longer than the second time.

A sixth aspect of the invention relates to a starting method of anengine mounted in a vehicle capable of running using torque output froman electric motor. This starting method includes detecting powerrequested by a driver; estimating efficiency of a hybrid system thatincludes the electric motor and the engine, when the engine is driven torealize the power requested by the driver; comparing a time for whichthe engine continues to be stopped with a first time and a second timethat is longer than the first time; determining whether the estimatedefficiency is equal to or greater than a preset efficiency, when thetime for which the engine continues to be stopped is longer than thefirst time and shorter than the second time; and starting the enginewhen the time for which the engine continues to be stopped is longerthan the second time.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a block diagram schematically showing a plug-in hybridvehicle;

FIG. 2 is a diagram (part 1) of an electrical system of the plug-inhybrid vehicle;

FIG. 3 is another diagram (part 2) of the electrical system of theplug-in hybrid vehicle;

FIG. 4 is a view of a connector of a charge cable;

FIG. 5 is a graph showing a range in which a CS mode is selected and arange in which a CD mode is selected;

FIG. 6 is a graph showing the periods of time when the engine is stoppedand periods of time when the engine is driven;

FIG. 7 is a flowchart illustrating the control structure of a routineexecuted by an ECU according to a first example embodiment of theinvention;

FIG. 8 is a view of a map used for setting and estimating the enginespeed and output;

FIG. 9 is a flowchart illustrating the control structure of a routineexecuted by the ECU according to a second example embodiment of theinvention;

FIG. 10 is a view of a map used for estimating efficiency;

FIG. 11 is a flowchart illustrating the control structure of a routineexecuted by the ECU according to a third example embodiment of theinvention; and

FIG. 12 is a view of the engine state at various fuel efficiencies.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example embodiments of the present invention will be described ingreater detail below with reference to the accompanying drawings. In thefollowing description, like parts will be denoted by like referencecharacters and referred to by the same nomenclature and have the samefunctions. Therefore, detailed descriptions of those parts will not berepeated.

First Example Embodiment

A plug-in hybrid vehicle is provided with an engine 100, a firstmotor-generator 110, a second motor-generator 120, a power split device130, a reduction gear 140, and a battery 150, as shown in FIG. 1.

The engine 100, the first motor-generator 110, the secondmotor-generator 120, and the battery 150 are all controlled by an ECU(Electronic Control Unit) 170. The ECU 170 may also be divided into aplurality of ECUs.

This vehicle runs using torque from at least one of the engine 100 orthe second motor-generator 120. That is, one or both of the engine 100and the second motor-generator 120 is automatically selected as thedrive source according to the operating state.

For example, when the accelerator operation amount is small or when thevehicle speed is low or the like, the plug-in hybrid vehicle runs usingonly the second motor-generator 120 as the drive source. In this case,the engine 100 is stopped.

Also, when the accelerator operation amount is large, when the vehiclespeed is high, or when the state-of-charge (SOC) of the battery 150 islow or the like, the engine 100 is driven. In this case, the plug-inhybrid vehicle runs using only the engine 100 or both the engine 100 andthe second motor-generator 120 as the drive source.

Moreover, this vehicle runs switching between a CS (Charge Sustaining)mode and a CD (Charge Depleting) mode automatically, for example.Incidentally, the CS mode and the CD mode may also be switched manually.

In the CS mode, the plug-in hybrid vehicle runs while maintaining theelectric power stored in the battery 150 at a predetermined targetvalue.

In the CD mode, the plug-in hybrid vehicle runs mainly using only thedriving force of the second motor-generator 120 using electric power,and does not maintain the electric power stored in the battery 150 forrunning. However, in the CD mode, when the accelerator operation amountis high or when the vehicle speed is high or the like, the engine 100may be driven to provide assist driving force.

The CS mode may also be referred to as an HV mode. Similarly, the CDmode may also be referred to as an EV mode. The CS mode and the CD modewill both be described in greater detail later.

The engine 100 is an internal combustion engine. A crankshaft thatserves as an output shaft is rotated by the combustion of an air-fuelmixture in a combustion chamber. Exhaust gas discharged from the engine100 is discharged out of the vehicle after first being purified by acatalyst 102. The catalyst 102 displays a purifying effect by beingwarmed up to a specific temperature. The catalyst 102 is warmed up usingthe heat of the exhaust gas. The catalyst 102 is a three-way catalyst,for example.

The plug-in hybrid vehicle is also provided with an oil pump 106 that isconnected to the output shaft of the engine 100 so as to be driven bythe engine 100. The oil pump 106 pumps oil to lubricate the axles andthe differential gear and the like of the drive train.

The engine 100, the first motor-generator 110, and the secondmotor-generator 120 are all connected via the power split device 130.Power generated by the engine 100 is split into two paths by the powersplit device 130. One path is a path for driving front wheels 160 viathe reduction gear 140. The other path is a path for driving the firstmotor-generator 110 to generate electric power.

The first motor-generator 110 is a three-phase alternating current motorthat has three coils, i.e., a U-phase coil, a V-phase coil, and aW-phase coil. The first motor-generator 110 generates electric powerusing power from the engine 100 that has been split by the power splitdevice 130. The electric power generated by the first motor-generator110 is used as the situation demands according to the running state ofthe vehicle and the SOC of the battery 150. For example, during normalrunning, the electric power generated by the first motor-generator 110is used directly to drive the second motor-generator 120. On the otherhand, when the SOC of the battery 150 is lower than a preset value, theelectric power generated by the first motor-generator 110 is convertedfrom alternating current to direct current by an inverter that will bedescribed later. Then the voltage is regulated by a converter that willalso be described later, and the power is stored in the battery 150.

When the first motor-generator 110 is used as a generator, the firstmotor-generator 110 generates negative torque. Here, negative torquerefers to torque that becomes a negative load on the engine 100. Whenthe first motor-generator 110 receives a supply of power and functionsas a motor, the first motor-generator 110 generates positive torque.Here, positive torque is torque that does not become a load on theengine 100, i.e., torque that assists with the rotation of the engine100. Incidentally, this is also true for the second motor-generator 120.

The second motor-generator 120 is a three-phase alternating currentmotor that has three coils, i.e., a U-phase coil, a V-phase coil, and aW-phase coil. The second motor-generator 120 is driven by at least oneof electric power stored in the battery 150 or electric power generatedby the first motor-generator 110.

The driving force of the second motor-generator 120 is transmitted tothe front wheels 160 via the reduction gear 140. Accordingly, the secondmotor-generator 120 assists the engine 100 or runs the vehicle using thedriving force from the second motor-generator 120. That is, the plug-inhybrid vehicle can be run using the electric power stored in the battery150. Incidentally, rear wheels may be driven instead of, or in additionto, the front wheels 160.

During regenerative braking of the plug-in hybrid vehicle, the secondmotor-generator 120 is driven by the front wheels 160 and the secondmotor-generator 120 operates as a generator. As a result, the secondmotor-generator 120 operates as a regenerative brake that convertsbraking energy into electric power. The electric power generated by thesecond motor-generator 120 is stored in the battery 150.

The power split device 130 is formed by a planetary gear set thatincludes a sun gear, pinion gears, a carrier, and a ring gear. Thepinion gears are in mesh with the sun gear and the ring gear. Thecarrier rotatably supports the pinion gears. The sun gear is connectedto a rotating shaft of the first motor-generator 110. The carrier isconnected to the crankshaft of the engine 100. The ring gear isconnected to a rotating shaft of the second motor-generator 120 and tothe reduction gear 140.

Because the engine 100, the first motor-generator 110, and the secondmotor-generator 120 are all connected via the power split device 130formed by a planetary gear, the relationship of the rotation speeds ofthe engine 100, the first motor-generator 110, and the secondmotor-generator 120 is one in which the rotation speeds are connected bya straight line in an alignment graph. That is, the firstmotor-generator 110 is connected to the output shaft of the engine 100via the power split device 130.

The battery 150 is a battery pack formed by a plurality of batterymodules, each of which is formed by a plurality of battery cellsintegrated together, that are connected together in series. The voltageof the battery 150 is approximately 200 V, for example. Power suppliedfrom an external power supply outside the vehicle, aside from the firstmotor-generator 110 and the second motor-generator 120, is charged tothe battery 150. Incidentally, a capacitor may be used instead of, or inaddition to, the battery 150.

The electrical system of the plug-in hybrid vehicle will now bedescribed in greater detail with reference to FIG. 2. The plug-in hybridvehicle includes a converter 200, a first inverter 210, a secondinverter 220, an SMR (System Main Relay) 230, a charger 240, and aninlet 250.

The converter 200 includes a reactor, two npn-type transistors, and twodiodes. One end of the reactor is connected to a positive terminal sideof each battery, and the other end of the reactor is connected to aconnecting point of the two npn-type transistors.

The two npn-type transistors are connected in series. The npn-typetransistors are controlled by the ECU 170. A diode is connected betweena collector and emitter of each npn-type transistor such that currentflows from the emitter side to the collector side.

Incidentally, IGBTs (Insulated Gate Bipolar Transistors), for example,may be used as the npn-type transistors. Instead of thenpn-type-transistors, power switching elements such as power MOSFETs(Metal Oxide Semiconductor Field-Effect Transistors) may be used.

When supplying electric power discharged from the battery 150 to thefirst motor-generator 110 or the second motor-generator 120, the voltageis stepped up by the converter 200. Conversely, when charging electricpower generated by the first motor-generator 110 or the secondmotor-generator 120 to the battery 150, the voltage is stepped down bythe converter 200.

A system voltage VH between the converter 200 and the inverters isdetected by a voltage sensor 180. The detection result of the voltagesensor 180 is output to the ECU 170.

The first inverter 210 includes a U-phase arm, a V-phase arm, and aW-phase arm. The U-phase arm, the V-phase arm, and the W-phase arm areconnected in parallel. The U-phase arm, the V-phase arm, and the W-phasearm each have two npn-type transistors that are connected in series. Adiode that allows current to flow from an emitter side to a collectorside is connected between a collector and emitter of each npn-typetransistor. The connecting point of each npn-type transistor of each armis connected at an end portion that is different from a neutral point112 of each coil of the first motor-generator 110.

The first inverter 210 converts direct current supplied from the battery150 into alternating current and then supplies this alternating currentto the first motor-generator 110. Also, the first inverter 210 convertsalternating current generated by the first motor-generator 110 intodirect current.

The second inverter 220 includes a U-phase arm, a V-phase arm, and aW-phase arm. The U-phase arm, the V-phase arm, and the W-phase arm areconnected in parallel. The U-phase arm, the V-phase arm, and the W-phasearm each have two npn-type transistors that are connected in series. Adiode that allows current to flow from an emitter side to a collectorside is connected between a collector and emitter of each npn-typetransistor. The connecting point of each npn-type transistor of each armis connected at an end portion that is different from a neutral point112 of each coil of the second motor-generator 120.

The second inverter 220 converts direct current supplied from thebattery 150 into alternating current and then supplies this alternatingcurrent to the second motor-generator 120. Also, the second inverter 220converts alternating current generated by the second motor-generator 120into direct current.

The converter 200, the first inverter 210, and the second inverter 220are all controlled by the ECU 170.

The SMR 230 is provided between the battery 150 and the charger 240. TheSMR 230 is a relay that switches between a state in which the battery150 is connected with the electrical system and a state in which thebattery 150 is disconnected from the electrical system. When the SMR 230is open, the battery 150 is disconnected from the electrical system.When the SMR 230 is closed, the battery 150 is connected to theelectrical system.

That is, when the SMR 230 is open, the battery 150 is electricallydisconnected from the converter 200 and the charger 240 and the like.When the SMR 230 is closed, the battery 150 is electrically connected tothe converter 200 and the charger 240 and the like.

The state of the SMR 230 is controlled by the ECU 170. For example, whenthe ECU 170 is turned on, the SMR 230 closes. When the ECU 170 is turnedoff, the SMR 230 opens.

The charger 240 is connected between the battery 150 and the converter200. As shown in FIG. 3, the charger 240 includes an AC/DC convertercircuit 242, a DC/AC converter circuit 244, an insulated transformer246, and a rectifier circuit 248.

The AC/DC converter circuit 242 is formed from a single phase bridgecircuit. The AC/DC converter circuit 242 converts alternating current(AC) power into direct current (DC) power based on a drive signal fromthe ECU 170. Moreover, the AC/DC converter circuit 242 also functions asa step-up chopper circuit that steps up the voltage by using the coil asa reactor.

The DC/AC converter circuit 244 is formed from a single phase bridgecircuit. The DC/AC converter circuit 244 converts DC power into highfrequency AC power based on a drive signal from the ECU 170, and outputsthis high frequency AC power to the insulated transformer 246.

The insulated transformer 246 includes a core made of magnetic material,and a primary coil and a secondary coil that are wound around the core.The primary coil and the secondary coil are electrically insulated andare connected to the DC/AC converter circuit 244 and the rectifiercircuit 248, respectively. The insulated transformer 246 converts highfrequency AC power received from the DC/AC converter circuit 244 to avoltage level corresponding to the turn ratio of the primary coil andthe secondary coil, and outputs it to the rectifier circuit 248. Therectifier circuit 248 then rectifies the AC power output from theinsulated transformer 246 to DC power.

The voltage between the AC/DC converter circuit 242 and the DC/ACconverter circuit 244 (i.e., the voltage between terminals of asmoothing capacitor) is detected by a voltage sensor 182 and a signalindicative of the detection result is received by the ECU 170. Also, theoutput current of the charger 240 is detected by a current sensor 184and a signal indicative of the detection result is received by the ECU170. Further, the temperature of the charger 240 is detected by atemperature sensor 186, and a signal indicative of the detection resultis received by the ECU 170.

When the battery 150 is charged from an external power supply outsidethe vehicle, the ECU 170 generates a drive signal to drive the charger240 and outputs it to the charger 240.

Other than functioning to control the charger 240, the ECU 170 alsofunctions to detect a failure of the charger 240. A failure of thecharger 240 is detected when, for example, the voltage detected by thevoltage sensor 182, the current detected by the current sensor 184, orthe temperature detected by the temperature sensor 186, becomes equal toor greater than a threshold value.

The inlet 250 is provided on a side portion of the plug-in hybridvehicle, for example. A connector 310 of a charge cable 300 thatconnects the plug-in hybrid vehicle with an external power supply 402outside the plug-in hybrid vehicle connects to the inlet 250.

The charge cable 300 that connects the plug-in hybrid vehicle to theexternal power supply 402 includes the connector 310, a plug 320, and aCCID (Charging Circuit Interrupt Device) 330.

The connector 310 of the charge cable 300 connects to the inlet 250provided in the plug-in hybrid vehicle. The connector 310 is providedwith a switch 312. When the switch 312 is closed while the connector 310of the charge cable 300 is connected to the inlet 250 provided in theplug-in hybrid vehicle, a connector signal CNCT indicating that theconnector 310 of the charge cable 300 is connected to the inlet 250provided in the plug-in hybrid vehicle is input to the ECU 170.

The switch 312 opens and closes in conjunction with a retaining piece316 that retains the connector 310 of the charge cable 300 in the inlet250 of the plug-in hybrid vehicle. The retaining piece 316 pivots inresponse to the operator pushing a button 314 provided on the connector310.

For example, when the operator releases a finger from the button 314 ofthe connector 310, shown in FIG. 4, while the connector 310 of thecharge cable 300 is connected to the inlet 250 provided in the plug-inhybrid vehicle, the retaining piece 316 engages with the inlet 250provided in the plug-in hybrid vehicle, and the switch 312 closes. Whenthe operator presses the button 314, the retaining piece 316 disengagesfrom the inlet 250, and the switch 312 opens. Incidentally, the methodfor opening and closing the switch 312 is not limited to this.

Returning now to FIG. 3, the plug 320 of the charge cable 300 connectsto an outlet 400 provided in a house or the like. AC power from theexternal power supply 402 outside the plug-in hybrid vehicle is suppliedto the outlet 400.

The CCID 330 has a relay 332 and a control pilot circuit 334. When thecontrol pilot circuit 334 is open, the path that supplies power from theexternal power supply 402 outside the plug-in hybrid vehicle to theplug-in hybrid vehicle is interrupted. When the relay 332 is closed,power is able to be supplied from the external power supply 402 outsidethe plug-in hybrid vehicle to the plug-in hybrid vehicle. The state ofthe relay 332 is controlled by the ECU 170 while the connector 310 ofthe charge cable 300 is connected to the inlet 250 of the plug-in hybridvehicle.

The control pilot circuit 334 outputs a pilot signal (i.e., arectangular wave signal) CPLT to a control pilot line when the plug 320of the charge cable 300 is connected to the outlet 400, i.e., isconnected to the external power supply 402, and the connector 310 isconnected to the inlet 250 provided in the plug-in hybrid vehicle. Thepilot signal is oscillated from an oscillator provided in the controlpilot circuit 334.

When the plug 320 of the charge cable 300 is connected to the outlet400, the control pilot circuit 334 is able to output a constant pilotsignal CPLT even if the connector 310 is disconnected from the inlet 250provided in the plug-in hybrid vehicle. However, the ECU 170 is unableto detect a pilot signal CPLT output when the connector 310 isdisconnected from the inlet 250 provided in the plug-in hybrid vehicle.

When the SMR 230 of the charge cable 300 is connected to the outlet 400and the connector 310 is connected to the inlet 250 of the plug-inhybrid vehicle, the control pilot circuit 334 oscillates a pilot signalCPLT of a preset pulse width (i.e., duty cycle).

The current capacity that is able to be supplied is reported to theplug-in hybrid vehicle by the pulse width of the pilot signal CPLT. Forexample, the current capacity of the charge cable 300 is reported to theplug-in hybrid vehicle. The pulse width of the pilot signal CPLT isconstant and does not rely on the voltage and the current of theexternal power supply 402.

Meanwhile, the pulse width of the pilot signal CPLT may differ if adifferent type of charge cable is used. That is, the pulse width of thepilot signal CPLT may be set for each type of charge cable.

In this example embodiment, power supplied from the external powersupply 402 is charged to the battery 150 while the plug-in hybridvehicle is connected to the external power supply 402 by the chargecable 300. During charging of the battery 150, the SMR 230 and the relay332 in the CCID 330 are closed.

An AC voltage VAC of the external power supply 402 is detected by avoltage sensor 188 provided in the plug-in hybrid vehicle. A signalindicative of the detected voltage VAC is output to the ECU 170.

Next, the CS mode and the CD mode will be described in greater detailwith reference to FIG. 5. The ECU 170 determines which mode to selectfrom among the CS mode and the CD mode. For example, the CS mode isselected if the SOC of the battery 150 is equal to or less than athreshold value. The CD mode is selected if the SOC of the battery 150is greater than the threshold value.

More specifically, the CS mode is selected if the SOC of the battery 150is equal to or less than a threshold value, or if the electrical systemof the plug-in hybrid vehicle stopped the last time with the CS modebeing selected.

The CD mode is selected if the SOC of the battery 150 is greater thanthe threshold value and there is a history of the battery 150 beingcharged by the external power supply 402 outside the plug-in hybridvehicle, or if the SOC of the battery 150 is greater than the thresholdvalue and the electrical system of the plug-in hybrid vehicle stoppedthe last time with the CS mode being selected. Charging of the battery150 is controlled by the ECU 170, so the determination as to whetherthere is a history of the battery 150 having been charged by theexternal power supply 402 outside the plug-in hybrid vehicle is made inthe ECU 170 using a flag or the like for example. Incidentally, themethod for selecting the CS mode and the CD mode is not limited to this.

In the CS mode and the CD mode, the plug-in hybrid vehicle runs by thedriving force of at least one of the engine 100 or the secondmotor-generator 120.

As shown in FIG. 6, if the running power of the plug-in hybrid vehicleis less than an engine startup threshold value, the plug-in hybridvehicle runs using only the driving force of the second motor-generator120.

If, on the other hand, the running power of the plug-in hybrid vehicleis equal to or greater than the engine startup threshold value, theengine 100 is driven. As a result, the plug-in hybrid vehicle runs usingthe driving force of the engine 100 in addition to, or instead of, thedriving force of the second motor-generator 120. Also, the powergenerated by the first motor-generator 110 using the driving force ofthe engine 100 is supplied directly to the second motor-generator 120.The time T for which the engine 100 continues to be stopped is measuredby a counter in the ECU 170, for example.

The running power is calculated by the ECU 170 according to a map havingthe operation amount of an accelerator pedal that is operated by adriver (i.e., the accelerator operation amount) and the vehicle speed orthe like, for example, as parameters. That is, in this exampleembodiment, the running power of the plug-in hybrid vehicle representsthe power requested by the driver. Incidentally, the method ofcalculating the running power is not limited to this.

The plug-in hybrid vehicle is controlled such that the running power isrealized shared by the engine 100 and the second motor-generator 120.For example, when the first motor-generator 110 is not generating power,the sum of the output power of the engine 100 and the output power ofthe second motor-generator 120 is controlled to be substantially equalto the running power. Therefore, if the output power of the engine 100is zero, the output power of the second motor-generator 120 iscontrolled to be substantially equal to the running power. Also, if theoutput power of the second motor-generator 120 is zero, the output powerof the engine 100 is controlled to be substantially equal to the runningpower. Incidentally, the manner in which the output power is controlledis not limited to this.

The engine startup threshold value in the CD mode is larger than theengine startup threshold value in the CS mode. That is, the region inwhich the engine 100 is stopped and the plug-in hybrid vehicle runs byonly the driving force of the second motor-generator 120 in the CD modeis larger than the region in which the engine 100 is stopped and theplug-in hybrid vehicle runs by only the driving force of the secondmotor-generator 120 in the CS mode. Accordingly, in the CD mode, theengine 100 is stopped and the plug-in hybrid vehicle is controlled torun by mainly only the driving force of the second motor-generator 120.On the other hand, the frequency with which the engine 100 is driven inthe CS mode is higher than the frequency with which the engine 100 isdriven in the CD mode. Therefore, in the CS mode, the plug-in hybridvehicle is controlled to run efficiently using both the engine 100 andthe second motor-generator 120.

The power charged to the battery 150 in the CD mode is less than thepower charged to the battery 150 in the CS mode. More specifically, inthe CS mode, the charging power of the battery 150 is determinedaccording to the SOC of the battery 150. The engine 100 is driven suchthat power corresponding to the determined charging power can begenerated using the first motor-generator 110. On the other hand, in theCD mode, the charging power of the battery 150 is normally determined tobe zero. That is, in the CD mode, the power obtained by regenerativebraking is charged to the battery 150, but the engine 100 is not drivento charge the battery 150.

Therefore, in the CD mode, power stored in the battery 150, inparticular, power supplied from the external power supply 402 outsidethe plug-in hybrid vehicle, is actively consumed.

Accordingly, if the battery 150 is frequently charged using the externalpower supply 402 outside the plug-in hybrid vehicle, and the plug-inhybrid vehicle is driven such that the running power does not exceed theengine startup threshold value, the engine 100 may not be driven for anextended period of time.

Therefore, in this example embodiment, if the period of time duringwhich the engine 100 continues to be stopped becomes long, the engine100 is forcibly started.

A routine executed by the ECU 170 will now be described with referenceto FIG. 7. The following routine is executed when a hybrid system isturned on, for example. This routine may be realized by software or byhardware.

In step S100, the ECU 170 determines whether the time T for which theengine 100 has remained stopped is equal to or less than a thresholdvalue T1. If the time T for which the engine 100 has remained stopped isequal to or less than the threshold value T1 (i.e., YES in step S100),this cycle of the routine ends. If, however, the time T for which theengine 100 has remained stopped is longer than the threshold value T1(i.e., NO in step S100), the process proceeds on to step S102.

Incidentally, instead of determining whether the time T for which theengine 100 has remained stopped is equal to or less than the thresholdvalue T1, it may be determined whether an amount of evaporated fuel(i.e., an amount of fuel vapor) from a fuel tank, not shown, that istrapped in a canister, also not shown, is equal to or less than athreshold value A1. The amount of fuel vapor becomes larger as the timeT for which the engine 100 continues to be stopped becomes longer, sothe time T for which the engine 100 continues to be stopped can beindirectly evaluated using the amount of fuel vapor. The method forcalculating the amount of fuel vapor may be any known typical method, soa detailed description thereof will not be repeated here.

In step S102, the ECU 170 determines whether the time T for which theengine 100 continues to be stopped is equal to or less than a thresholdvalue T2 that is longer than the threshold value T1. If the time T forwhich the engine 100 continues to be stopped is equal to or less thanthe threshold value T2 (i.e., YES in step S102), the process proceeds onto step S104. If, on the other hand, the time T for which the engine 100continues to be stopped is longer than the threshold value T2 (i.e., NOin step S102), the process moves ahead to step S108.

Incidentally, instead of determining whether the time T for which theengine 100 has remained stopped is equal to or less than the thresholdvalue T2, it may be determined whether an amount of evaporated fuel(i.e., an amount of fuel vapor) from a fuel tank, not shown, that istrapped in a canister, also not shown, is equal to or less than a secondthreshold value A2 that is larger than the threshold value A1.

In step S104, the ECU 170 estimates an engine speed NE and an outputtorque TE of the engine when the engine 100 is driven in order torealize the running power of the plug-in hybrid vehicle, i.e., torealize the power requested by the driver.

In this example embodiment, because the engine 100 is controlled torealize the engine speed NE and the output torque TE set according tothe power requested of the engine 100, the engine speed NE and theoutput torque TE are estimated using the running power of the plug-inhybrid vehicle as the power requested of the engine 100.

In this example embodiment, the engine speed NE and the output torque TEare determined by the intersection of a curve set to realize the optimumfuel efficiency and a constant power line, as shown in FIG. 8, forexample. That is, the engine speed NE and the output torque TE thatrealize the best fuel efficiency are selected from among the enginespeed NE and the output torque TE that realize the requested power.

A map used to set and estimate the engine speed NE and the output torqueTE is created in advance by the developer based on test and simulationresults. Incidentally, the method for estimating the engine speed NE andthe output torque TE is not limited to this.

Returning now to FIG. 7, in step S106, the ECU 170 determines whetherthe estimated engine speed NE is greater than a first speed NE1 and lessthan a second speed NE2 that is greater than the first speed NE1, andwhether the estimated output torque TE is greater than a first torqueTE1 and less than a second torque TE2 that is greater than the firsttorque TE1.

Incidentally, the operating range in which the engine speed NE isgreater than the first speed NE1 and less than the second speed NE2, andin which the output torque TE of the engine is greater than the firsttorque TE1 and less than the second torque TE2 is a range that isdetermined to have good fuel efficiency based on the results of testsand simulations and the like.

If the estimated engine speed NE is greater than the first speed NE1 andless than the second speed NE2 that is greater than the first speed NE1,and the estimated output torque TE is greater than the first torque TE1and less than the second torque TE2 that is greater than the firsttorque TE1 (i.e., YES in step S106), the process proceeds on to stepS108. If not (i.e., NO in step S106), then this cycle of the routineends.

In step S108, the ECU 170 determines whether the remaining amount offuel (such as gasoline, gas oil, or alcohol fuel) stored in the fueltank is equal to or greater than a preset threshold value. If theremaining amount of fuel is equal to or greater than the threshold value(i.e., YES in step S108), the process proceeds on to step S110. If not(i.e., NO in step S108), then this cycle of the routine ends.

In step S110, the ECU 170 starts the engine 100. The manner in which theengine 100 according to this example embodiment is controlled will nowbe described based on the structure and flowchart described above.

If the time T for which the engine 100 continues to be stopped is longerthan the threshold T1 (i.e., NO in step S100) and also longer than thethreshold value T2 (i.e., NO in step S102), the engine 100 is forciblystarted (step S110). As a result, the oil pump 106 can be driven, so thedrive train and the like can be sufficiently lubricated.

If, on the other hand, the time T for which the engine 100 continues tobe stopped is longer than the threshold value T1 (i.e., NO in step S100)and equal to or less than the threshold value T2 (i.e., YES in stepS102), the engine speed NE and the output torque TE are estimated whenthe engine 100 is driven to realize the running power of the plug-inhybrid vehicle (step S104).

If the estimated engine speed NE is greater than the first speed NE1 andless than the second speed NE2 that is greater than the first speed NE1,and the estimated output torque TE is greater than the first torque TE1and less than the second torque TE2 that is greater than the firsttorque TE1 (i.e., YES in step S106), then it is determined whether theremaining amount of fuel stored in the fuel tank is equal to or greaterthan a preset threshold value (step S108). If the remaining amount offuel is equal to or greater than the threshold value (i.e., YES in stepS108), then the engine 100 is started (step S110). As a result, theengine 100 can be forcibly started in an operating range with good fuelefficiency.

Second Example Embodiment

Hereinafter, a second example embodiment of the invention will bedescribed. In the second example embodiment, the engine 100 is driven inan operating state (such as the output torque and rotation speed) inwhich the efficiency of the engine 100 is equal to or greater than apreset efficiency. The other aspects of the second example embodimentare the same as those of the first example embodiment, so detaileddescriptions thereof will not be repeated here.

A routine executed by the ECU 170 will now be described with referenceto FIG. 9. The following routine is executed when a hybrid system isturned on, for example. This routine may be realized by software or byhardware. Steps in this routine that are the same as those in theroutine of the first example embodiment will be denoted by the same stepnumbers, so detailed descriptions thereof will not be repeated here.

In step S200, the ECU 170 estimates the efficiency of the engine 100according to the estimated engine speed NE and the estimated outputtorque TE. As shown in FIG. 10, the efficiency is estimated according toa map having the engine speed NE and the output torque TE, for example,as parameters. The map is created in advance by the developer based onthe results of tests and simulations and the like. Incidentally, themethod for estimating the efficiency is not limited to this.

Returning now to FIG. 9, in step S202, the ECU 170 determines whetherthe estimated efficiency is equal to or greater than a presetefficiency. If the estimated efficiency is equal to or greater than thepreset efficiency (i.e., YES in step S202), the routine proceeds on tostep S108. If not (i.e., NO in step S202), then this cycle of theroutine ends.

With this structure as well, effects that are substantially similar tothose obtained by the first example embodiment are able to be obtained.

Third Example Embodiment

Hereinafter, a third example embodiment of the invention will bedescribed. In the third example embodiment, the engine 100 is driven inan operating state in which the efficiency of a hybrid system thatincludes the engine 100, the first motor-generator 110, and the secondmotor-generator 120 is equal to or greater than a preset efficiency. Theother aspects of the third example embodiment are the same as those ofthe first or second example embodiment, so detailed descriptions thereofwill not be repeated here.

A routine executed by the ECU 170 will now be described with referenceto FIG. 11. The following routine is executed when the hybrid system isturned on, for example. This routine may be realized by software or byhardware. Steps in this routine that are the same as those in theroutine of the first example embodiment will be denoted by the same stepnumbers, so detailed descriptions thereof will not be repeated here.

In step S300, the ECU 170 estimates the efficiency of the hybrid systemthat includes the engine 100, the first motor-generator 110, and thesecond motor-generator 120. The efficiency of the hybrid system assumingthat the second motor-generator 120 is not being operated is estimated,for example. That is, the sum of the efficiency of the engine 100 andthe efficiency of the first motor-generator 110 is calculated. When theengine 100 is forcibly driven, it is assumed that the running power ofthe vehicle is realized by only the engine 100, so the efficiency of thehybrid system assuming that the second motor-generator 120 is not beingoperated is estimated.

The efficiency is estimated according to a map of the relationship ofthe efficiency and various operating states (such as the output torqueand rotation speed), that is created based on the results of tests andsimulations and the like, for example.

In step S302, the ECU 170 determines whether the estimated efficiency isequal to or greater than a preset efficiency. If the estimatedefficiency is equal to or greater than a preset efficiency (i.e., YES instep S302), the process proceeds on to step S108. If not (i.e., NO instep S302), then this cycle of the process ends.

With this structure as well, effects that are substantially similar tothose obtained by the first or second example embodiment are able to beobtained.

Other Example Embodiments

At least one of the engine speed NE or the output torque TE may bechanged to increase the efficiency of the engine 100 after starting theengine 100 in the first through the third example embodiments. Forexample, the starting point of the engine 100 may be changed from A to Bto improve fuel efficiency, as shown in FIG. 12. As a result, the amountof fuel consumed is able to be further reduced.

Also, the ratio of the output power of the engine 100 and the outputpower of the second motor-generator 120 may be changed to increase theefficiency of the engine 100. For example, the output power of theengine 100 may be reduced to increase the efficiency of the engine 100,and the output power of the second motor-generator 120 may be increasedby the amount that the output power of the engine 100 is reduced.Conversely, the output power of the engine 100 may be increased toincrease the efficiency of the engine 100, and the output power of thesecond motor-generator 120 may be reduced by the amount that the outputpower of the engine 100 is increased. As a result, the amount of fuelconsumed is able to be further reduced, and fluctuation in output powerof the vehicle as a whole is able to be suppressed.

While the invention has been described with reference to exampleembodiments thereof, it is to be understood that the invention is notlimited to the described embodiments or constructions. The invention isintended to cover various modifications and equivalent arrangements. Inaddition, while the various elements of the disclosed invention areshown in various example combinations and configurations, othercombinations and configurations, including more, less or only a singleelement, are also within the scope of the appended claims.

1. (canceled)
 2. A starting system of an engine mounted in a vehiclecapable of running using torque output from an electric motor,comprising: a detection portion that detects power requested by adriver; a estimation portion that estimates efficiency of the enginewhen the engine is driven to realize the power requested by the driver;a comparing portion that compares a time for which the engine continuesto be stopped with a first time and a second time that is longer thanthe first time; a determining portion that determines whether theestimated efficiency is equal to or greater than a preset efficiency,when the time for which the engine continues to be stopped is longerthan the first time and shorter than the second time; a starting portionthat starts the engine when the estimated efficiency is equal to orgreater than the preset efficiency; and a second starting portion thatstarts the engine when the time for which the engine continues to bestopped is longer than the second time. 3-4. (canceled)
 5. The startingsystem of an engine according to claim 2, further comprising: a portionthat changes at least one of the engine speed or the output torque toincrease efficiency of the engine. 6-7. (canceled)
 8. The startingsystem of an engine according to claim 2, further comprising: a portionthat changes a ratio of output power of the engine and output power ofthe electric motor to increase efficiency of the engine. 9-10.(canceled)
 11. The starting system of an engine according to claim 2,wherein the comparing portion includes a portion that compares the timefor which the engine continues to be stopped with the first time and thesecond time, by comparing an amount of fuel vapor of the engine with afirst amount and a second amount that is greater than the first amount.12-13. (canceled)
 14. A starting method of an engine mounted in avehicle capable of running using torque output from an electric motor,comprising: detecting power requested by a driver; estimating efficiencyof the engine when the engine is driven to realize the power requestedby the driver; comparing a time for which the engine continues to bestopped with a first time and a second time that is longer than thefirst time; determining whether the estimated efficiency is equal to orgreater than a preset efficiency, when the time for which the enginecontinues to be stopped is longer than the first time and shorter thanthe second time; starting the engine when the estimated efficiency isequal to or greater than the preset efficiency; and starting the enginewhen the time for which the engine continues to be stopped is longerthan the second time.
 15. (canceled)